This invention relates to a disk brake of a type including:
a pusher movable toward and away from a friction surface defined on at least one brake disk;
spring means urging the pusher away from the friction surface;
at least one bush sliding in interference fit within a corresponding seat of the pusher and adapted to abut on an abutment surface of the brake to limit a return stroke of the pusher away from the friction surface; and
at least one corresponding link acting between said bush and said abutment surface to limit the bush travel relatively to said abutment surface such that it be a predetermined distance effective to define, with the brake released, a predetermined clearance between the pusher and the friction surface.
A brake having such features is known from the Applicant's production.
Traditional hydraulically operated brakes, specifically intended for application to axles of agricultural tractors or industrial vehicles, have provisions for keeping the clearance between the pusher and the friction surfaces substantially constant with the brake released. This clearance is necessary to allow for free rotation of the disks and to prevent wear of the friction surfaces with the brake released, and would tend to increase in use of the brake as a result of the friction surfaces undergoing progressive wear. Any uncontrolled increase of this clearance is bound to cause increased length of the stroke required to bring the pusher to contact the friction surfaces, and hence increased oil requirements to apply the brake. This increased requirement for oil may in certain circumstances exceed the capacity of the brake pump (customarily foot operated) provided for delivering oil under a pressure to the actuator that actuates the pusher. In that case, one stroke of the brake pedal would be inadequate to immediately and effectively apply it, which results in an obviously hazardous situation for the user. In all cases, the stroke length of the brake pedal will increase progressively over time.
The above-mentioned provisions include a plurality of bushes, sliding in interference fit within respective seats and adapted to be pulled by the pusher (through corresponding links) during the brake application stroke, only after a predetermined active travel of the pusher. This predetermined active travel, or loose movement of the pusher before the bushes begins pulled, is substantially equal to the normal clearance provided in the rest condition between the pusher and the friction surfaces, and is determined by the difference between the axial length of the bushes and the distance of the heads of the corresponding links from an abutment surface of the brake.
Presently, this distance is heavily affected by machining tolerances, especially axial dimension tolerances, of different components, among which the bushes, the link shanks, the washers interposed between the link heads and the corresponding bushes, and between the link bases and the pusher surface.
Owing to said components interleaving with one another, individual tolerances add up with the brake in the assembled condition, and the overall dimensional error may grow enough to again affect proper operation of the brake.
On the other hand, any recourse to closer limits for the admissible machining tolerances of each component would unavoidably reflect in unacceptably increased costs, and interfere with the possibility to use standard production parts, such as for the screws that form the links.